<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <script src="./vue.js"></script>
</head>
<body>
  <div id="app">
    <!-- input的v-model的原理 -->
    <input type="text" :value="username" @input="handleUsernameInput">
    {{username}}
  </div>
  <script>
    const app = new Vue({
      el: '#app',
      data: {
        username: ''
      },
      methods: {
        handleUsernameInput (e) {
          this.username = e.target.value
        }
      }
    })
  </script>
</body>
</html>
